This invention relates to a lens plate for an optical sensor device in a vehicle, in particular for a rain sensor, with a transmitter-side lens structure and a receiver-side lens structure.
Rain sensors in vehicles, which detect the wetting of a pane, include a light transmitter, a lens plate attached to the pane with a coupling layer, and a light receiver. The lens plate includes a transmitter-side and a receiver-side lens structure, which each consist of a light input and a light output structure.
The light emitted by the light transmitter is coupled into the lens plate by means of the transmitter-side light input structure and converted to substantially parallel light beams which vertically traverse the lens plate. The transmitter-side light output structure deflects the light bundle by about 45°, so that after traversing the coupling layer and the glass it reaches the outer surface thereof. There, the light bundle is totally reflected and again traverses glass and coupling layer. The receiver-side light input structure again directs the light bundle vertically through the lens plats, before it is focused onto the surface of the light receiver by the receiver-side light output structure.
During wetting of the surface of the pane, a part of the light is coupled out at the surface of the pane. Thus, only a part of the light is reflected. By means of the variation of the intensity of the reflected light which is reflected back onto the light receiver, the wetting of the pane thus can be detected.
In the lens plates known from the prior art, the light distribution on the windshield, however, is not uniform, but has a distinct peak in the middle and a strong decrease towards the edge. Wetting in the edge region, in which the light intensity is distinctly lower, thus leads to a lower loss of light than wetting in the middle of the measurement region. Wetting in the edge region thus is hard to detect due to the small light difference. The surface which can be utilized for defecting the wetting of the pane thus is substantially smaller than the actually illuminated surface.